Can you use Portlets / Portal to make a dashboard coming from multiple Databases?

I was wondering if it is possible to make a Portal that would display report information in a dashboard format (charts, red/yellow/green lights, etc). The example in the first chapter of the Portlets in Action seem to point to yes.

Can you connect things like multiple Excel spreadsheets? Does it have to be DB based? Can you connect to things that are not in Java?

I suppose most important for me -- does this book cover the questions I have about with examples?

And, of course, as the 1st chapter indicates, a portal may not be the best solution? Is a dashboard to simple to need a portal? Would a gadget or stand alone webapp be easier (as far as learning curve?) Does the book cover how to develop Mashups or only Portlets?

Wow -- another question...heh -- Is Liferay the recommended system for Portlets or the only system for Portlets (or neither I suppose...)

Dashboard is an ideal candidate for using portlets. But, a few things you need to think about the requirement of the dashboard before deciding on using portlets:
1- Is the dashboard data comes from different information sources ( different databases can be considered as different information sources ) ?
2- Does the dashboard provides any personalization/customization features to its users ?
3- Does an action on a dashboard data-window affects content of the data contained in one/more data-windows ?

Can you connect things like multiple Excel spreadsheets? Does it have to be DB based? Can you connect to things that are not in Java? - You can connect to things that are not in Java. Multiple excel sheets embedded in a web page can't be considered as different information sources. Its not necessary that the information is DB backed, you can have information that you retrieved using an external web service or any other external system.

Chapter 1 which is available for download contains information on when to use portals and when not to use them. Chapter 1 talks about Mashups and how they are a good fit to be developed using portlets but it doesn't contain examples of it.

Liferay is an open-source portal server. There are other portal servers that you can also consider - GateIn, IBM WebSphere Portal, and so on.